The present invention relates generally to the projection of laser beams for the directional aiming of apparatus such as radiometer instruments, which may be used for ascertaining the temperature of a surface using infra-red measurement techniques, and more particularly to such apparatus which utilises a laser sighting device arranged to project one or more laser sighting beams onto a target for identifying on the surface of the target an energy zone thereof, the temperature of which is to be measured.
It is useful, in the operation of such laser beam projection apparatus, to have the facility to change the number and/or configuration of beams which are issued from the laser beam projector.
By way of example, in a first case it may be desirable to have a single beam which is axial and which gives rise to a single central illuminated spot on the target area to be investigated. In a second case it may be desirable to have a plurality of laser beams which produce illuminated spots on, for example, the periphery of a target area of a surface to be investigated. The selected production of a single spot, by a single laser beam, and of a plurality of spots by a plurality of laser beams, is conveniently arranged by providing a beam splitter, which may be for example a diffraction lens or grid, which can be brought into and out of operation with respect to a single laser beam produced by the beam generator.
When a single laser beam is divided, by the beam splitter, into a plurality of beams, there is a corresponding proportional lowering of the strength of each of the plurality of beams, as compared with that of the single central beam. According to the degree of sub-division of the single beam, the strength of each of the plurality of beams may then become too low to be of practical use, i.e. the illumination provided by each of them on the surface of the target may be too weak to see clearly, especially in bright ambient light, or at a relatively long distance which may be essential in the investigation of a target surface which is at a very high temperature.
It is not possible to overcome this factor of change of intensity, as between the single beam and the plurality of beams by merely increasing proportionately the power of the single beam when it is to be subdivided, because there are legal and practical restrictions on the use of laser beams because of the possible danger to the user, e.g. the damaging of eyesight. A requirement currently in force for a Class IIIA Laser Diode is that the maximum output be less than 5 milliwatts.
It is known in practice in the art to utilise hand-held instruments, such as radiometers, which incorporate a laser beam generator for aiming a beam, or beams, at a target area, and a heat-sensitive device for measuring the radiation which is emitted by the targeted area of a heated surface. Unless provision can be made for changing of the strength of the laser beam, there is always a limitation of (a) the number of beams which can usefully be obtained from splitting of a single beam, and (b) the effectiveness of the instrument, used with a distant target, because of the resultant relatively lowered illuminating power of each of the beams which is split from the original single beam.
It is a first object of the invention to provide an improvement, to laser beam projection instruments having provision for projecting a single, e.g. axial, beam and for dividing that single beam into a plurality of beams, by which the relative power of the single beam, and of the plurality of beams, can be varied so that the power of the multiple beams can be increased while still remaining within acceptable limits.
It is a second object of the invention to provide an improvement, in laser beam projection instruments, whereby the power of the single beam is variable at its stage of generation such that its power may be at an acceptable level while the single beam is being used, and may be increased when a plurality of beams are produced, to enhance the utility of the instrument at a distance from a target, while nevertheless keeping the power of the plural beams at acceptable level.
It is a third object of the invention to provide an improvement, in laser beam projection instruments, whereby the power of the single beam is made initially substantially higher than would be safe if used along so as, when it is sub-divided into a plurality of beams, to permit that plurality of beams each to have a usefully enhanced power, and whereby the power of the single beam is reduced by attenuation, when used as a single beam, so as to remain within acceptable limits.